QS Study

The cerebrum is convex and is related to the cranial vault. It is about 2-5 mm thick and accounts for about 80% of the brain’s totaling mass. Functions include thinking and reasoning, memory, consciousness, attention, perceptual awareness and language.

Classification of nerve fibers of cerebrum –

  1. Association (arcuate) fibers.
  2. Projection fibers.
  3. Commissural fibers.

(A) Association Fibers

These are the fibers which connect different cortical areas of the same hemisphere to one another. These fibers are axons that connect cortical areas within the same cerebral hemisphere.


  • Short association fibers: Connect adjacent gyri.
  • Long association fibers: Connect gyri that lie further apart.

Examples –

(a) The uncinate fasciculus: Connecting the temporal pole to the motor speech area and to the orbital cortex.

(b) The cingulum: Connecting the cingulate gyros to the parahippocampal gyrus.

(c) The superior longitudinal fasciculus: Connecting the frontal lobe to occipital and temporal lobes.

(d) The inferior longitudinal fasciculus: Connecting the occipital & temporal lobes.

Fibers of Cerebrum 1

Fig: Nerve Fibers of Cerebrum

(B) Projection fibers

These are fibers which connect the cerebral cortex to another part of the CNS, e.g., the brainstem and spinal cord. These fibers are consist of efferent and afferent fibers uniting the cortex with the lower parts of the brain and with the spinal cord. Examples –

  • Corticospinal tracts.
  • Corticopontine tracts.

(C) Commissural Fibers

These are the fibers which connect corresponding parts of the two hemispheres. These fibers are axons that connect the two hemispheres of the brain. They are –

(1) The corpus callosum: Connect the cerebral cortex of the two sides.

(2) The anterior commissure: Connect the archipallium of the two sides.

(3) The posterior commissure: Connect the superior colliculi of the two sides.

(4) Fornix: Connect the crura of the fornix of two sides.

(5) The habenular commissure: Connect the habenular nuclei.

(6) Hypothalamic commissures: Connect the two cerebral hemispheres.

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